How do you 'hollow out' a motherboard? and were would you buy the chip's from?
You take it out...simple.
For the GTX480Ms, you should be able get it from here ( http://www.mxm-upgrade.com/
) soon. Or just buy 2 HD5870s now...
(Notice the quotes, "fitting" doesn't mean it "works", it simply "fits".. lol)